The invention relates to a method of transmitting teletext pages, in which a table is transmitted in which a code for consecutive decimally numbered teletext pages is accommodated in successive columns of consecutive rows. The invention also relates to a teletext transmission station and a teletext receiver.
A method of the type mentioned in the opening paragraph is described on pages 76-83 of "Teletext Specification", Interim Technical Document SPB 492 published by the European Broadcasting Union in December 1992. More particularly, this document describes a TOP page (Table Of Pages) in which a code is incorporated for the decimally numbered teletext pages. This code indicates, for example for each page whether this page is actually transmitted or whether it is the first of a group of pages about a given subject, or whether it is a rotating page, and the like. There are two versions of the TOP page, a first version with codes for all 800 teletext pages and a version with codes for the 100 teletext pages of a teletext magazine. A teletext magazine is formed by the plurality of pages having the same start digit. For example, there is a TOP page for the page numbers in the range between 100 and 199, a TOP page for the page numbers in the range between 200 and 299, etc.
The codes are accommodated in rows and columns at the character positions of the TOP page. More particularly the forty character positions of the first text row of the TOP page comprise the code for the teletext pages 100-139, the forty character codes of the second text row comprise the code for the teletext pages 140-179, etc. Thus, 800 codes for the pages 100-899 are accommodated in twenty rows. In the magazine version of the TOP page, 100 codes are accommodated in 3 rows. In the known method, the position of the code for a given teletext page can be established by means of a simple computing operation.
The known TOP page comprises only the codes for the teletext pages having a decimal page number. This is understood to mean a page number which is built up of the digits 0-9 which can be selected by means of the keys on a conventional hand-held remote-control unit. As is assumed to be known, the tens and units of a teletext page number are, however, constituted by a 4-bit digit which may assume 16 values. For some applications it is conventional practice to transmit teletext pages with a page number, one or more digits of which are outside the range of 0-9. In this connection it is common practice to speak of hexadecimal page numbers. Examples are 10A-10F, 1A0-1AF, 1F0-1FF. Hexadecimal page numbers cannot be called with the conventional hand-held remote-control unit. They are used to transmit additional information such as enhancement data for upgrading a standard page to a higher display level. The term "extension page" will hereinafter be often used for hexadecimal pages and "basic page" for the decimal pages.